Cyclobutane benzene derivatives

ABSTRACT

PCT No. PCT/EP93/03112 Sec. 371 Date Jul. 20, 1994 Sec. 102(e) Date Jul. 20, 1994 PCT Filed Nov. 8, 1993 PCT Pub. No. WO94/12455 PCT Pub. Date Jun. 9, 1994.The invention relates to methylenecyclobutane benzene derivatives of the formula I     &lt;IMAGE&gt; n have the meaning given in claim 1, and to their use as components of liquid-crystalline media for electrooptical displays.

SUMMARY OF THE INVENTION

The invention relates to cyclobutane benzene derivatives of the formulaI ##STR2## in which

R¹ is alkyl or alkenyl having 1 to 16 carbon atoms, in whichadditionally one or more CH₂ groups may be replaced by --O--, or is agroup of the formula ##STR3## in which

R² is alkyl or alkenyl having 1 to 16 carbon atoms, ##STR4##

O is 0 or 1,

V and W are each CH₂ or CH₂ CH₂, and when V is CH₂ CH₂ m is 1, 2 or 3and W is CH₂,

A¹ is at each occurrence, independently of the others, 1,4-phenylenewhich is unsubstituted or substituted by 1 to 2 fluorine atoms, inwhich, in addition, one or two CH groups may be replaced by N, or is1,4-cyclohexylene which is unsubstituted or substituted by a cyanogroup, and in which, in addition, one or two CH₂ groups may be replacedby O or S, or is thiadiazole-2,5-diyl, 1,4-bicyclo[2.2.2]-octylene, or aradical of the formula ##STR5##

L¹ and L² are each independently of one another H or F,

Z¹ is --CO--O--, --O--CO--, --CH₂ O--, --OCH₂ --, --CH₂ CH₂ --, --C≡C--or a single bond,

Y is NCS, halogen or an alkyl, alkoxy, alkenyl or alkenyloxy grouphaving 1 to 8 carbon atoms which is substituted by at least one fluorineand/or chlorine atom,

and, if m=1, 2 or 3, is CN, or alkyl, or alkenyl having up to 16 carbonatoms, in which, in addition, 1 or more CH₂ groups may be reacted [sic]by --O--,

m is 0, 1, 2 or 3, and

n is 0, 1 or 2.

The invention relates furthermore to the use of these compounds ascomponents of liquid-crystalline media and to liquid-crystal andelectrooptical display elements containing the liquid-crystalline mediaaccording to the invention.

The compounds of the formula I can be used as components ofliquid-crystalline media, especially for displays which are based on theprinciple of the twisted cell, including their highly twisted variants,for example STN or SBE, on the guest-host effect, on the effect of thedeformation of aligned phases or on the effect of dynamic scattering.

The object underlying the invention was to discover new, stable,liquid-crystalline or mesogenic compounds which are suitable ascomponents of liquid-crystalline media and which, in particular, have acomparatively low viscosity and a moderate positive dielectricanisotropy.

It has now been found that compounds of the formula I are ideally suitedas components of liquid-crystalline phases. In particular, they possesscomparatively low viscosities. They can be used to obtain stableliquid-crystalline phases with a broad mesophase range and advantageousvalues for the optical and dielectric anisotropy, which are at the sametime notable for highly favorable values for specific resistance and lowviscosities. By this means it is possible, in particular, to attaindefinite advantages in media for active matrix displays or supertwistdisplays.

Japanese Published Application JP 02 085 243 discloses benzonitrilederivatives of the formula ##STR6## (n=1 or2).

GB 21 55 946 encompasses cyclobutane derivatives of the formula I, butonly describes cyclobutanecarboxylic esters. These esters, however, arenot suitable for active matrix displays.

Other similar cyclobutane derivatives are described by:

DE-A 37 17 484: ##STR7##

DE-A 39 29 524: ##STR8##

The general formula of WO 91/08184 includes benzene derivatives whichhave a group ##STR9## However, no cyclobutane derivatives are describedtherein.

Furthermore, the compounds described in the prior art only have moderatevalues for their optical anisotropy, whereas the compounds according tothe invention possess distinctly lower optical anistropies andviscosities.

The provision of compounds of the formula I moreover represents, inquite general terms, a considerable broadening of the range ofliquid-crystalline substances which are suitable, subject to variousperformance-related criteria, for the preparation of liquid-crystallinemixtures.

The compounds of the formula I possess a broad range of application.Depending on the choice of substituents these compounds can be used asbase materials, of which liquid-crystalline phases are predominantlycomposed; however, it is also possible to add compounds of the formula Ito liquid-crystalline base materials from other classes of compound, inorder, for example, to influence the dielectric and/or opticalanisotropy of such a dielectric and/or to optimize its threshold voltageand/or its viscosity.

The compounds of the formula I are colorless in the pure state and formliquid-crystalline mesophases in a temperature range which is favorablefor electrooptical use. They are stable chemically, thermally and withrespect to light.

The invention therefore relates to the compounds of the formula I.

Preferred embodiments of the present invention are:

a) derivatives in which m is 0;

b) derivatives in which L¹ and L² are identical and are F;

c) derivatives of the formula I1, ##STR10## in which R¹, A¹, Z¹ and Yhave the meaning given; d) derivatives of the formula I2, ##STR11## inwhich R¹ and A¹ have the meaning given; e) derivatives of the formulaI3, ##STR12## in particular of the formula I3a ##STR13## in which R²,A¹, Z¹, V, W, L¹, L², m, n and Y have the meaning given.

The invention furthermore relates to the use of these compounds ascomponents of liquid-crystalline media. The invention relatesfurthermore to liquid-crystalline media containing at least onecompound; and to liquid-crystal display elements, especiallyelectrooptical display elements, which contain such media, especiallymatrix liquid-crystal displays.

PREFERRED EMBODIMENTS

For simplicity, Cbu below is a radical of the formula ##STR14##

A³ is a radical of the formula ##STR15##

Cyc is a 1,4-cyclohexylene radical, Che is a 1,4-cyclohexylene radical,Dio is a 1,3-dioxane-2,5-diyl radical, Dit is a 1,3-dithiane-2,5-diylradical, Phe is a 1,4-phenylene radical, PheF is a 1,4-phenylene radicalwhich is mono- or disubstituted by fluorine, Pyd is a pyridine-2,5-diylradical, Pyr is a pyrimidine2,5-diyl [sic] radical and Bi is abicyclo[2.2.2]octylene radical, where Cyc and/or Phe are unsubstitutedor may be mono- or disubstituted by F or CN.

The compounds of the formula I correspondingly include compoundscontaining two rings, of the subformula Ia:

    R.sup.1 --Cbu--A.sup.3 --Y                                 Ia

compounds containing three rings, of the subformulae Ib to Ig:

    R.sup.1 --Cbu--A.sup.1 --A.sup.3 --Y                       Ib

    R.sup.1 --Cbu--A.sup.1 --Z1--A.sup.3 --Y [sic]             Ic

    R.sup.2 --Cyc--Cbu--A.sup.3 --Y                            Id

    R.sup.2 --Dio--Cbu--A.sup.3 --Y                            Ie

    R.sup.2 --Cyc--CH.sub.2 CH.sup.2 --Cbu--A.sup.3 --Y [sic]  If

    R.sup.2 --Dio--CH.sub.2 CH.sub.2 --Cbu--A.sup.3 --Y        Ig

and compounds containing four rings, of the subformulae Ih to Iq:

    R.sup.1 --Cbu--A.sup.1 --A.sup.1 --A.sup.3 --Y             Ih

    R.sup.1 --Cbu--A.sup.1 --Z.sup.1 --A.sup.1 --A.sup.3 --Y   Ii

    R.sup.1 --Cbu--A.sup.1 --A.sup.1 --Z.sup.1 --A.sup.3 --Y   Ij

    R.sup.1 --Cbu--A.sup.1 --Z.sup.1 --A.sup.1 --Z.sup.1 --A.sup.3 --YIk

    R.sup.2 --Cyc--Cbu--A.sup.1 --A.sup.3 --Y                  Il

    R.sup.2 --Dio--Cbu--A.sup.1 --A.sup.3 --Y                  Im

    R.sup.2 --Cyc--Cbu--A.sup.1 --Z.sup.1 --A.sup.3 --Y        In

    R.sup.2 --Dio--Cbu--A.sup.1 --Z.sup.1 --A.sup.3 --Y        Io

    R.sup.2 --Cyc--CH.sub.2 CH.sub.2 --Cbu--A.sup.1 --A.sup.3 --YIp

    R.sup.2 --Dio--CH.sub.2 CH.sub.2 --Cbu--A.sup.1 --A.sup.3 --YIq

Of these compounds, those of the subformulae Ia, Ib, Ic, Id, Ie, If, Ig,Ii and Il are particularly preferred.

The preferred compounds of the subformula Ia include those of thesubformulae Iaa and Iab:

    R.sup.1 --Cbu--Phe--Y                                      Iaa

    R.sup.1 --Cbu--Phe--F--Y                                   Iab

Of these compounds, those of the formula Iab are particularly preferred.

The preferred compounds of the subformula Ib include those of thesubformulae Iba to Ibf:

    R.sup.1 --Cbu--Phe--Phe--Y                                 Iba

    R.sup.1 --Cbu--Phe--PheF--Y                                Ibb

    R.sup.1 --Cbu--Cyc--Phe--Y                                 Ibc

    R.sup.1 --Cbu--Cyc--PheF--Y                                Ibd

    R.sup.1 --Cbu--PheF--Phe--Y                                Ibe

    R.sup.1 --Cbu--PheF--PheF--Y                               Ibf

The preferred compounds of the subformula Ic include those of thesubformulae Ica to Ich:

    R.sup.1 --Cbu--Phe--Z.sup.1 --Phe--Y                       Ica

    R.sup.1 --Cbu--Phe--Z.sup.1 --PheF--Y                      Icb

    R.sup.1 --Cbu--Cyc--Z.sup.1 --Phe--Y                       Icc

    R.sup.1 --Cbu--Cyc--Z.sup.1 --PheF--Y                      Icd

    R.sup.1 --Cbu--Dio--Z.sup.1 --Phe--Y                       Ice

    R.sup.1 --Cbu--Dio--Z.sup.1 --PheF--Y                      Icf

    R.sup.1 --Cbu--Pyd--Z.sup.1 --A.sup.3 --Y                  Icg

    R.sup.1 --Cbu--Pyr--Z.sup.1 --A.sup.3 --Y                  Ich

Of these compounds, those of the formulae Ica, Icb and Icc areparticularly preferred.

The preferred compounds of the subformula Id include those of thesubformulae Ida and Idb:

    R.sup.2 --Cyc--Cbu--Phe--Y                                 Ida

    R.sup.2 --Cyc--Cbu--PheF--Y                                idb

The preferred compounds of the subformula Ie include those of thesubformulae Iea and Ieb:

    R.sup.2 --Dio--Cbu--Phe--Y                                 Iea

    R.sup.2 --Dio--Cbu--PheF--Y                                Ieb

In the compounds of the formulae above and below, the radicals L¹ and L²are identical or different from one another; they are preferablyidentical and are F.

The terminal group R¹ --Cbu is preferably a group of the formulae 1 to7: ##STR16## in which the radicals Cbu² and Cbu⁵ are particularlypreferred.

A¹ is preferably Phe, Cyc, Pyr or Dio. The compounds of the formula Ipreferably contain not more than one of the radicals Bi, Pyd, Pyr, Dioor Dit.

Also preferred are compounds of the formula I and of all subformulae inwhich A¹ and/or A³ is 1,4-phenylene which is mono- or disubstituted byF. In particular these are 2-fluoro-1,4-phenylene,3-fluoro-1,4-phenylene and 2,3-difluoro-1,4-phenylene,2,6-difluoro-1,4-phenylene and 3,5-difluoro-1,4-phenylene.

Particularly preferred compounds of the formulae I are those in which A³is 1,4-phenylene which is unsubstituted or mono- or disubstituted by F.

The group A³ --Y is preferably: ##STR17## in which alkyl is alkyl having1 to 16 carbon atoms.

Preferred radicals A³ are those in which at least one of the ligands L¹and L² is F, in particular in which L¹ and L² are F.

Z¹ is preferably a single bond, --CO--O--, --O--CO-- and --CH₂ CH₂ --,with a secondary preference for --CH₂ O--, --OCH₂ --.

If R¹ or Y is an alkyl radical, then this radical may be straight-chainor branched. It is preferably straight-chain, has 2, 3, 4, 5 or 6 carbonatoms and is therefore preferably ethyl, propyl, butyl, pentyl or hexyl.

If R¹ or Y is an alkenyl radical, then this radical may bestraight-chain or branched. It is preferably branched, has 2, 3, 4, 5 or6 carbon atoms and is therefore vinyl, allyl, prop-1-enyl, but-1-(2- or3-)enyl, pent-1-(2-, 3- or 4-)enyl, hex-1-(2-, 3-, 4- or 5-)enyl.

If Y is an alkoxy radical, then this radical is branched orstraight-chain.

It is preferably straight-chain and is therefore preferably methoxy,ethoxy, propoxy, butoxy, pentyloxy or heptyloxy.

L¹ and L² are preferably identical and are F or H, especially F.

Among these compounds of the formula I and the subformulae, those arepreferred in which at least one of the radicals they contain has one ofthe preferred meanings given.

In the compounds of the formula I those stereoisomers are preferred inwhich the rings Cyc and piperidine are trans-1,4-disubstituted. Those ofthe abovementioned formulae which contain one or more groups Pyd, Pyr,Dit and/or Dio in each case include the two 2,5-positional isomers.

Particularly preferred compounds of the formula I which contain a groupof the formula 1 are those of the subformulae I1a to I1p:

    R.sup.1 --Cbu.sup.1 --Phe--F                               I1a

    R.sup.1 --Cbu.sup.1 --PheF--F                              I1b

    R.sup.1 --Cbu.sup.1 --Phe--NCS                             I1c

    R.sup.1 --Cbu.sup.1 --PheF--NCS                            I1d

    R.sup.1 --Cbu.sup.1 --Phe--OCF.sub.3                       I 1e

    R.sup.1 --Cbu.sup.1 --PheF--OCF.sub.3                      I 1f

    R.sup.1 --Cbu.sup.1 --Phe--OCF.sub.2 H                     I1g

    R.sup.1 --Cbu.sup.1 --PheF--OCF.sub.2 H                    I1h

    R.sup.1 --Cbu.sup.1 --Cyc--Phe--F                          I1i

    R.sup.1 --Cbu.sup.1 --Cyc--PheF--F                         I1j

    R.sup.1 --Cbu.sup.1 --Cyc--PheF--NCS                       I1k

    R.sup.1 --Cbu.sup.1 --Cyc--Phe--NCS                        I1l

    R.sup.1 --Cbu.sup.1 --Cyc--Phe--OCF.sub.3                  I 1m

    R.sup.1 --Cbu.sup.1 --Cyc--Phe--OCF.sub.2 H                I1n

    R.sup.1 --Cbu.sup.1 --Cyc --PheF--OCF.sub.3                I 1o

    R.sup.1 --Cbu.sup.1 --Cyc --PheF--OCF.sub.2 H              I1p

Particularly preferred compounds of the formula I which contain a groupof the formula 2 are those of the subformulae I2a to I2x:

    R.sup.1 --Cbu.sup.2 --Phe--F                               I2a

    R.sup.1 --Cbu.sup.2 --PheF--F                              I2b

    R.sup.1 --Cbu.sup.2 --Phe--NCS                             I2c

    R.sup.1 --Cbu.sup.2 --PheF--NCS                            I2d

    R.sup.1 --Cbu.sup.2 --Phe--OCF.sub.3                       I 2e

    R.sup.1 --Cbu.sup.2 --PheF--OCF.sub.3                      I 2f

    R.sup.1 --Cbu.sup.2 --Phe--OCF.sub.2 H                     I2g

    R.sup.1 --Cbu.sup.2 --PheF--OCF.sub.2 H                    I2h

    R.sup.1 --Cbu.sup.2 --Cyc--Phe--F                          I2i

    R.sup.1 --Cbu.sup.2 --Cyc--PheF--F                         I2j

    R.sup.1 --Cbu.sup.2 --Cyc--PheF--NCS                       I2k

    R.sup.1 --Cbu.sup.2 --Cyc--Phe--NCS                        I2l

    R.sup.1 --Cbu.sup.2 --Cyc--Phe--OCF.sub.3                  I 2m

    R.sup.1 --Cbu.sup.2 --Cyc--Phe --OCF.sub.2 H               I2n

    R.sup.1 --Cbu.sup.2 --Cyc--PheF--OCF.sub.2 H               I2o

    R.sup.1 --Cbu.sup.2 --Cyc--PheF--OCF.sub.3                 I 2p

    R.sup.1 --Cbu.sup.2 --Phe--alkyl                           I2q

    R.sup.1 --Cbu.sup.2 --Phe--Oalkyl                          I2r

    R.sup.1 --Cbu.sup.2 --Cyc--Phe--alkyl                      I2s

    R.sup.1 --Cbu.sup.2 --Cyc--Phe--Oalkyl                     I2t

    R.sup.1 --Cbu.sup.2 --Phe--CN                              I2u

    R.sup.1 --Cbu.sup.2 --PheF--CN                             I2v

    R.sup.1 --Cbu.sup.2 --CycPhe--CN                           I2w

    R.sup.1 --Cbu.sup.2 --Cyc--PheF--CN                        I2x

Particularly preferred compounds of the formula I which contain a groupof the formula 3 are those of the subformulae I3a to I3p:

    R.sup.1 --Cbu.sup.3 --Phe--F                               I3a

    R.sup.1 --Cbu.sup.3 --PheF--F                              I3b

    R.sup.1 --Cbu.sup.3 --Phe--NCS                             I3c

    R.sup.1 --Cbu.sup.3 --PheF--NCS                            I3d

    R.sup.1 --Cbu.sup.3 --Phe--OCF.sub.3                       I 3e

    R.sup.1 --Cbu.sup.3 --PheF--OCF.sub.3                      I 3f

    R.sup.1 --Cbu.sup.3 --Phe--OCF.sub.2 H                     I3g

    R.sup.1 --Cbu.sup.3 --PheF--OCF.sub.2 H                    I3h

    R.sup.1 --Cbu.sup.3 --Cyc--Phe--F                          I3i

    R.sup.1 --Cbu.sup.3 --Cyc--PheF--F                         I3j

    R.sup.1 --Cbu.sup.3 --Cyc--PheF--NCS                       I3k

    R.sup.1 --Cbu.sup.3 --Cyc--Phe--NCS                        I3l

    R.sup.1 --Cbu.sup.3 --Cyc--Phe--OCF.sub.3                  I 3m

    R.sup.1 --Cbu.sup.3 --Cyc--Phe--OCF.sub.2 H                I3n

    R.sup.1 --Cbu.sup.3 --Cyc--PheF--OCF.sub.2 H               I3o

    R.sup.1 --Cbu.sup.3 --Cyc--PheF--OCF.sub.3                 I 3p

Particularly preferred compounds of the formula I which contain a groupof the formula 5 are those of the subformulae I5a to I5x:

    R.sup.2 --Cbu.sup.5 --Phe--F                               I5a

    R.sup.2 --Cbu.sup.5 --PheF--F                              I5b

    R.sup.2 --Cbu.sup.5 --Phe--NCS                             I5c

    R.sup.2 --Cbu.sup.5 --PheF--NCS                            I5d

    R.sup.2 --Cbu.sup.5 --Phe--OCF.sub.3                       I 5e

    R.sup.2 --Cbu.sup.5 --PheF--OCF.sub.3                      I 5f

    R.sup.2 --Cbu.sup.5 --Phe--OCF.sub.2 H                     I5g

    R.sup.2 --Cbu.sup.5 --PheF--OCF.sub.2 H                    I5h

    R.sup.2 --Cbu.sup.5 --Cyc--Phe--F                          I5i

    R.sup.2 --Cbu.sup.5 --Cyc--PheF--F                         I5j

    R.sup.2 --Cbu.sup.5 --Cyc--Phe--NCS                        I5k

    R.sup.2 --Cbu.sup.5 --Cyc--PheF--NCS                       I5l

    R.sup.2 --Cbu.sup.5 --Cyc--Phe--OCF.sub.3 --               I5m

    R.sup.2 --Cbu.sup.5 --Cyc--PheF--OCF.sub.3 --              I5n

    R.sup.2 --Cbu.sup.5 --Cyc--Phe--OCF.sub.2 H                I5o

    R.sup.2 --Cbu.sup.5 --Cyc--PheF--OCF.sub.2 H               I5p

    R.sup.2 --Cbu.sup.5 --Phe--CN                              I5q

    R.sup.2 --Cbu.sup.5 --PheF--CN                             I5r

    R.sup.2 --Cbu.sup.5 --CycPhe--CN                           I5s

    R.sup.2 --Cbu.sup.5 --Cyc--PheF--CN                        I5t

    R.sup.2 --Cbu.sup.5 --Cyc--Phe--Oalkyl                     I5u

    R.sup.2 --Cbu.sup.5 --Cyc--Phe--alkyl                      I5v

    R.sup.2 --Cbu.sup.5 --Phe--Oalkyl                          I5w

    R.sup.2 --Cbu.sup.5 --Phe--alkyl                           I5x

The 1,4-cyclohexenylene group preferably has the following structures:##STR18##

The compounds of the formula I are prepared by methods known per se, asdescribed in the literature (e.g. in the standard works such asHouben-Weyl, Methoden der Organischen Chemie [Methods of OrganicChemistry], Georg-Thieme-Verlag, Stuttgart, under reaction conditionswhich are known and suitable for the reactions mentioned. In thiscontext it is also possible to use variants which are known per se andnot mentioned here in any more detail.

The compounds of the formula I in which m is 0 may be prepared, forexample, in analogy in to that of Dobier et al. (J. Am. Chem. Soc. 107(12) 3626-31 (1985)) by cycloaddition of allenes with styrenederivatives and subsequent hydrogenation (cf. Scheme I): ##STR19##

In addition, the compounds of the formula I can be prepared from thecorresponding 3-substituted cyclobutanones by condensation with methanederivatives in accordance with C. Burton et al., Tetrahedron Lett. 29(24), 3003-6 (1988) or J. Fried, et al., Tetrahedron Lett. 25, 4329(1984) in the presence of a phosphine and subsequent hydrogenation (e.g.Schemes 2 to 5). ##STR20##

The compounds of the formula I3 can be prepared, for example, inaccordance with Scheme 6-8. ##STR21##

In addition, the compounds of the formula I can be prepared by reducinga compound which corresponds to the formula I except that, in place ofhydrogen atoms, it contains one or more reducible groups and/or C--Cbonds.

Suitable reducible groups which are preferred are carbonyl groups,especially keto groups, and also, for example, free or esterifiedhydroxyl groups or halogen atoms bonded to aromatic structures.Preferred starting materials for the reduction correspond to the formulaI but, in place of a cyclohexane ring, may contain a cyclohexene ring orcyclohexanone ring and/or in place of a --CH₂ CH₂ -- group may contain a--CH═CH-- group and/or in place of a --CH₂ -- group may contain a --CO--group and/or in place of a hydrogen atom may contain an OH group whichis free or functionally modified (e.g. in the form of its p-toluenesulfonate).

The reduction can be carried out, for example, by catalytichydrogenation at temperatures of between approximately 0° andapproximately 200° and at pressures of between approximately 1 and 200bar in an inert solvent, for example an alcohol such as methanol,ethanol or isopropanol, an ether such as tetrahydrofuran (THF) ordioxane, an ester such as ethyl acetate, a carboxylic acid such asacetic acid or a hydrocarbon such as cyclohexane. Suitable catalysts areadvantageously noble metals such as Pt or Pd, which may be employed inthe form of oxides (e.g. PtO₂, PdO), on a support (e.g. Pd on carbon,calcium carbonate or strontium carbonate) or in finely divided form.

Ketones can also be reduced by the methods of Clemmensen (with zinc,amalgamated zinc or tin and hydrochloric acid, advantageously inaqueous-alcoholic solution or in heterogeneous phase with water/tolueneat temperatures of between approximately 80° and 120°) or ofWolff-Kishner (with hydrazine, advantageously in the presence of alkalisuch KOH or NaOH in a high-boiling solvent such as diethylene glycol ortriethylene glycol at temperatures of between approximately 100° and200°) to give the corresponding compounds of the formula I which containalkyl groups and/or --CH₂ CH₂ -- bridges.

Reductions with complex hydrides are also possible. For example,arylsulfonyloxy groups can be reductively removed using LiAlH₄ and inparticular p-toluenesulfonyloxymethyl groups can be reduced to methylgroups, advantageously in an inert solvent such as diethyl ether or THFat temperatures of between approximately 0° and 100°. Double bonds canbe hydrogenated using NaBH₄ or tributyltin hydride in methanol.

Compounds of the formula I which correspond to the formula I exceptthat, in place of 1,4-phenylene radicals, they possess1,4-cyclohexenylene radicals, can be oxidized, for example, using DDQ(dichlorodicyanobenzoquinone) in a suitable solvent.

Esters of the formula I can also be obtained by esterification ofcorresponding carboxylic acids (or their reactive derivatives),especially of the formula IV, using alcohols or phenols (or theirreactive derivatives), in particular of the formula V, or by the DCCmethod (DCC=dicyclohexylcarbodiimide).

The corresponding carboxylic acids and alcohols or phenols are known orcan be prepared in analogy to known processes.

Particularly suitable reactive derivatives of the carboxylic acidsmentioned are the acid halides, especially the chlorides and bromides,and also the anhydrides, including, for example, mixed anhydrides,azides or esters, in particular alkyl esters having 1-4 carbon atoms inthe alkyl group.

Particularly suitable reactive derivatives of the alcohols and phenolsmentioned are the corresponding metal alcoholates or phenolates,preferably of an alkali metal such as sodium or potassium.

The esterification is advantageously carried out in the presence of aninert solvent. Particularly suitable such solvents are ethers such asdiethyl ether, di-n-butyl ether, THF, dioxane or anisole, ketones suchas acetone, butanone or cyclohexanone, amides such as DMF or phosphoricacid hexamethyltriamide, hydrocarbons such as benzene, toluene orxylene, halogenated hydrocarbons such as carbon tetrachloride,dichloromethane or tetrachloroethylene, and sulfoxides such as dimethylsulfoxide or sulfolane.

For the preparation of nitriles of the formula I it is possible todehydrate corresponding acid amides, for example those in which there isa CONH₂ group in place of the radical CN. The amides can be obtained,for example, from corresponding esters or acid halides by reaction withammonia. Examples of suitable water-eliminating agents are inorganicacid chlorides such as SOCl₂, PCl₃, PCl₅, POCl₃, SO₂ Cl₂, COCl₂, andalso P₂ O₅, P₂ S₅, AlCl₃ (for example as a double compound with NaCl),aromatic sulfonic acids and sulfonyl halides. This procedure can becarried out in the presence or absence of an inert solvent attemperatures of between approximately 0° and 150°; examples of suitablesolvents are bases such as pyridine or triethylamine, aromatichydrocarbons such as benzene, toluene or xylene, or amides such as DMF.

For the preparation of the abovementioned nitriles of the formula I itis also possible to react corresponding acid halides, preferably thechlorides, with sulfamide, advantageously in an inert solvent, forexample tetramethylenesulfone, at temperatures of between approximately80° and 150°, preferably at 120°. After conventional work-up thenitriles can be isolated directly.

Ethers of the formula I can be obtained by etherification ofcorresponding hydroxy compounds, in particular of the formula VI or VII,preferably corresponding Phenols, the hydroxy compound advantageouslybeing converted first into an appropriate metal derivative, for exampleby treatment with NaH, NaNH₂, NaOH, KOH, Na₂ CO₃ or K₂ CO₃ into thecorresponding alkali metal alcoholate or alkali metal phenolate. Thiscan then be reacted with the corresponding alkyl halide, alkyl sulfonateor dialkyl sulfate, advantageously in an inert solvent such as acetone,1,2-dimethoxyethane, DMF or dimethyl sulfoxide or else with an excess ofaqueous or aqueous-alcoholic NaOH or KOH at temperatures of betweenapproximately 20° and 100°.

For the preparation of nitriles of the formula I it is also possible toreact corresponding chlorine, bromine or iodine compounds of the formulaI with a cyanide, preferably with a metal cyanide such as NaCN, KCN orCu₂ (CN)₂, for example in the presence of pyridine in an inert solvent,for example DMF or N-methylpyrrolidone, at temperatures of between 20°and 200°.

Compounds of the formula I in which A¹ is substituted by at least onefluorine atom and/or one CN group can also be obtained from thecorresponding diazonium salts by exchange of the diazonium group for afluorine atom or for a CN group, for example by the methods of Schiemannor Sandmeyer.

Dioxane derivatives or dithiane derivatives of the formula I areadvantageously prepared by reacting a corresponding aldehyde (or one ofits reactive derivatives) with a corresponding 1,3-diol (or one of itsreactive derivatives) or, respectively, with a corresponding1,3-dithiol, preferably in the presence of an inert solvent such asbenzene or toluene and/or a catalyst, for example a strong acid such assulfuric acid, benzenesulfonic acid or p-toluenesulfonic acid, attemperatures between approximately 20° and approximately 150°,preferably between 80° and 120°. The principal reactive derivatives ofthe starting materials which are suitable are acetals.

The aldehydes and 1,3-diols or 1,3-dithiols mentioned and their reactivederivatives are in some cases known, while in other cases they can beprepared without difficulty, in accordance with standard methods oforganic chemistry, from compounds known from the literature. Forexample, the aldehydes can be obtained by oxidation of correspondingalcohols or by reduction of nitriles or corresponding carboxylic acidsor their derivatives, the diols by reduction of corresponding diesters,and the dithiols by reaction of corresponding dihalides using NaSH.

The liquid-crystalline media according to the invention preferablycontain, in addition to one or more compounds according to theinvention, from 2 to 40 further constituents, in particular from 4 to 30components. With very particular preference these media contain, inaddition to one or more compounds according to the invention, from 7 to25 components. These further constituents are preferably selected fromnematic or nematogenic (monotropic or isotropic ) substances, especiallysubstances from the classes of the azoxybenzenes, benzylideneanilines,biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl orcyclohexyl cyclohexanecarboxylates, phenyl or cyclohexyl cyclohexylbenzoates, phenyl or cyclohexyl cyclohexylcyclohexanecarboxylates,cyclohexylphenyl benzoates, cyclohexylphenyl cyclohexanecarboxylates orcyclohexylphenyl cyclohexylcyclohexanecarboxylates, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexylcyclohexenes,cyclohexylcyclohexylcyclohexenes, 1,4-bis-cyclohexylbenzenes,4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl-or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl- orcyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes,1-phenyl-2-cyclohexylethanes,1-cyclohexyl-2-(4-phenylcyclohexyl)ethanes,1-cyclohexyl-2-biphenylylethanes, 1-phenyl-2-cyclohexylphenylethanes,optionally halogenated stilbenes, benzyl phenyl ethers, tolans andsubstituted cinnamic acids. The 1,4-phenylene groups in these compoundsmay also be fluorinated.

The most important compounds suitable as further constituents of mediaaccording to the invention can be characterized by the formulae 1, 2, 3,4 and 5:

    R'--L--E--R"                                               1

    R'--L--COO--E--R"                                          2

    R'--L--OOC--E--R"                                          3

    R'--L--CH.sub.2 CH.sub.2 --E--R"                           4

    R'--L--C:C--E--R"                                          5

In the formulae 1, 2, 3, 4 and 5 L and E, which may be identical ordifferent, are in each case independently of one another a bivalentradical from the group formed by --Phe--, --Cyc--, --Phe--Phe--,--Phe--Cyc--, --Cyc--Cyc--, --Pyr--, --Dio--, --G--Phe-- and --G--Cyc--and their mirror images, in which Phe is 1,4-phenylene which isunsubstituted or substituted by fluorine, Cyc is trans-1,4-cyclohexyleneor 1,4-cyclohexenylene, Pyr is pyrimidine-2,5-diyl or pyridine-2,5-diyl,Dio is 1,3-dioxane-2,5-diyl and G is 2-(trans-1,4-cyclohexyl)ethyl,pyrimidine-2,5-diyl, pyridine-2,5-diyl or 1,3-dioxane-2,5-diyl.

Preferably, one of the radicals L and E is Cyc, Phe or Pyr. E ispreferably Cyc, Phe or Phe-Cyc. The media according to the inventionpreferably contain one or more components selected from the compounds ofthe formulae 1, 2, 3, 4 and 5 in which L and E are selected from thegroup Cyc, Phe and Pyr and at the same time one or more componentsselected from the compounds of the formulae 1, 2, 3, 4 and 5 in whichone of the radicals L and E is selected from the group Cyc, Phe and Pyrand the other radical is selected from the group --Phe--Phe--,--Phe--Cyc, --Cyc--Cyc--, --G--Phe-- and --G--Cyc--, and, if desired,one or more components selected from the compounds of the formulae 1, 2,3, 4 and 5 in which the radicals L and E are selected from the group--Phe--Cyc, --Cyc--Cyc--, --G--Phe-- and --G--Cyc--.

In the compounds of the subformulae 1a, 2a, 3a, 4a and 5a, R' and R"are, in each case independently of one another, alkyl, alkenyl, alkoxy,alkenyloxy or alkanoyloxy, having up to 8 carbon atoms. In the majorityof these compounds R' and R" are different from one another, with one ofthese radicals usually being alkyl or alkenyl. In the compounds of thesubformulae 1b, 2b, 3b, 4b and 5b R" is --CN, --CF₃ --OCF₃, --OCHF₂, F,Cl or --NCS; in this case R has the meaning given in the case of thecompounds of the subformulae 1a to 5a and is preferably alkyl oralkenyl. However, other variants of the substituents envisaged in thecompounds of the formulae 1, 2, 3, 4 and 5 can also be employed. Many ofthese substances, or alternatively mixtures thereof, are commerciallyavailable. All of these substances are obtainable by methods known fromthe literature or in analogy thereto.

The media according to the invention preferably contain, in addition tocomponents from the group of the compounds 1a, 2a, 3a, 4a and 5a (group1), components from the group of the compounds 1b, 2b, 3b, 4b and 5b(group 2), the proportions of which are preferably as follows:

Group 1: from 20 to 90%, in particular from 30 to 90%,

Group 2: from 10 to 80%, in particular from 10 to 50%,

the sum of the proportions of the compounds according to the inventionand the compounds from groups 1 and 2 giving a result of 100%.

The media according to the invention preferably contain from 1 to 40%,particularly preferably from 5 to 30%, of compounds according to theinvention. Of further preference are media which contain more than 40%,in particular from 45 to 90%, of compounds according to the invention.The media preferably contain three, four or five compounds according tothe invention.

The media according to the invention are prepared in a manner known perse. Generally the components are dissolved with one another,advantageously at elevated temperature. By appropriate additions theliquid-crystalline phases according to the invention can be modified sothat they can be used in all hitherto disclosed types of liquid-crystaldisplay elements.

Additives of this kind are known to the person skilled in the art andare described in detail in the literature (H. Kelker/R. Hatz, Handbookof Liquid Crystals, Verlag Chemie, Weinheim, 1980). For example,pleochroic dyes can be added to produce colored guest-host systems orsubstances can be added to alter the dielectric anisotropy, theviscosity and/or the orientation of the nematic phases.

Even without further comments it is assumed that a person skilled in theart can utilize the above description in the widest context. Thepreferred embodiments are, therefore, merely to be interpreted as adescriptive disclosure which should in no way be interpreted as in anyway limiting.

The complete disclosure content of all applications, patents andpublications listed above and below, and of the correspondingapplication P 42 39 169, filed on 21.11.92, are incorporated into thisapplication by reference. mp.=melting point, cp.=clear point. Above andbelow, percentages are percent by weight; all temperatures are given indegrees Celsius. "Conventional work-up" means: water is added, themixture is extracted with methylene chloride, the phases are separated,the organic phase is dried and concentrated by evaporation, and theproduct is purified by crystallization and/or chromatography.

Further definitions:

C: solid crystalline state, S: smectic phase (the index indicates thephase type), N: nematic state, Ch: cholesteric phase, I: isotropicphase. The number between two symbols indicates the transitiontemperature in degrees Celsius.

    ______________________________________                                        DAST           diethylaminosulfur trifluoride                                 DCC            dicyclohexylcarbodiimide                                       DDQ            dichlorodicyanobenzoquinone                                    DIBALH         diisobutylaluminum hydride                                     HMTAP          hexamethyltriaminophosphine                                    POT            potassium tert-butanolate                                      PCC            pyridinium chlorochromate                                      THF            tetrahydrofuran                                                TPP            triphenylphosphine                                             pTSOH          p-toluenesulfonic acid                                         ______________________________________                                    

EXAMPLES Example 1 Preparation of3-(3,4,5-trifluorophenyl)-1-methylcyclobutane

A) 3,4,5-Trifluorovinylbenzene

A mixture of 1 mol of 3,4,5-trifluorobromobenzene and 3 l of THF isadmixed at -70° C. with 1 mol of BuLi. Subsequently, a mixture of 0.5mol of zinc bromide in 1 l of THF is added to the reaction mixture, andthis mixture is stirred for 30 minutes at -65° C. Then 1 mol of vinylbromide and 0.022 mol of nickel(II) chloride/TPP is added.

The reaction mixture is stirred for 16 hours at room temperature andworked up in the conventional way. The resulting styrene derivative isprocessed further without purification.

B) 3-(3,4,5,-Trifluorophenyl)-2,2-dichlorocyclobutanone

A mixture of 0.25 mol of 1A, 23.0 g of zinc-copper (3% copper) and 800ml of diethyl ether is admixed over the course of 15 minutes with 0.25ml of trichloroacetyl chloride and the mixture is subsequently stirredunder reflux for 8 hours. After conventional work-up the product isobtained, which is processed further without purification.

C) 3-(3,4,5,-Trifluorophenyl)cyclobutanone

A mixture of 0.144 mol of 1B, 0.53 mol of zinc powder and 880 ml ofglacial acetic acid is stirred at room temperature for 17 hours. Afterconventional work-up the product is obtained, which is processed furtherwithout purification.

D) 3-(3,4,5,-(Trifluorophenyl)-1-methylenecyclobutane [sic]

A mixture of 0.15 mol of triphenylmethylenephosphine, 100 ml oftetraglyme and 0.13 mol of 1C [lacuna] added and stirred at roomtemperature for 16 hours. After conventional work-up and distillationfrom 100 ml of ethanol/ethyl acetate the pure product is obtained.

E) A mixture of 0.1 mol of 1D, 1 mmol of Pd/C (10%) and 100 ml oftoluene is hydrogenated to saturation at room temperature. Afterconventional work-up and chromatography the pure product is obtained.

The following are prepared analogously:

3-(3,4-Difluorophenyl)-1-methylcyclobutane

3-(4-Trifluoromethoxyphenyl)-1-methylcyclobutane

3-(3,5-Difluoro-4-difluoromethoxyphenyl)-1-methylcyclobutane

3-(3,4,5-Trifluorophenyl)-1-ethylcyclobutane

3-(3,4,5-Trifluorophenyl)-1-propylcyclobutane

3-(3,4,5-Trifluorophenyl)-1-butylcyclobutane

3-(3,4,5-Trifluorophenyl)-1-pentylcyclobutane

3-(3,4,5-Trifluorophenyl)-1-hexylcyclobutane

3-(3,4,5-Trifluorophenyl)-1-heptylcyclobutane

3-(3,4-Difluorophenyl)-1-ethylcyclobutane

3-(3,4-Difluorophenyl)-1-propylcyclobutane

3-(3,4-Difluorophenyl)-1-butylcyclobutane

3-(3,4-Difluorophenyl)-1-pentylcyclobutane

3-(3,4-Difluorophenyl)-1-hexylcyclobutane

3-(3,4-Difluorophenyl)-1-heptylcyclobutane

3-(-trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-1-methylcyclobutane [sic]

3-(-trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-1-ethylcyclobutane [sic]

3-(-trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-1-propylcyclobutane [sic]

3-(-trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-1-butylcyclobutane [sic]

3-(-trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-1-pentylcyclobutane [sic]

3-(-trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-1-hexylcyclobutane [sic]

3-(-trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-1-heptylcyclobutane [sic]

Example 2 6-(3,4,5-Trifluorophenyl)-2-methylspiro[3.3]heptane

2A) 7-(3,4,5-Trifluorophenyl)-1,1-dichlorospiro[3.3]-heptan-2-one

0.1 mol of 1D is reacted in accordance with Example 1B with 0.1 mol oftrichloroacetyl chloride. After conventional work-up the product isobtained, which is processed further without purification.

2B) 6-(3,4,5-Trifluorophenyl)spiro[3.3]heptan-2-one

A mixture of 0.075 mol of 2A and 0.25 mol of zinc powder is reacted inaccordance with Example 1C.

2C 6-(3,4,5-Trifluorophenyl)-2-methylenespiro[3.3]-heptane

0.05 mol of 2B is reacted in accordance with Example 1D with 0.06 mol oftriphenylphosphine. After conventional work-up and purification bychromatography the product is obtained.

2D) 0.02 mol of 2C is hydrogenated in accordance with Example 1E.

The following are prepared analogously:

6-(3,4-Difluorophenyl)-2-methylspiro[3.3]heptane

6-(4-Trifluoromethoxyphenyl)-2-methylspiro[3.3]heptane [sic]

6-(3,5-Difluoro-4-difluoromethoxyphenyl)-2-methylspiro-[3.3]heptane

6-(3,4,5-Trifluorophenyl)-2-ethylspiro[3.3]heptane

6-(3,4,5-Trifluorophenyl)-2-propylspiro[3.3]heptane, C 9 I

6-(3,4,5-Trifluorophenyl)-2-butylspiro[3.3]heptane

6-(3,4,5-Trifluorophenyl)-2-pentylspiro[3.3]heptane, C 11 I

6-(3,4,5-Trifluorophenyl )-2-hexylspiro[3.3]heptane

6-(3,4,5-Trifluorophenyl )-2-heptylspiro[3.3]heptane

6-(3,4-Difluorophenyl)-2-ethylspiro[3.3]heptane

6-(3,4-Difluorophenyl)-2-propylspiro[3.3]heptane

6-(3,4-Difluorophenyl)-2-butylspiro[3.3]heptane

6-(3,4-Difluorophenyl)-2-pentylspiro[3.3]heptane

6-(3,4-Difluorophenyl)-2-hexylspiro[3.3]heptane

6-(3,4-Difluorophenyl)-2-heptylspiro[3.3]heptane

6-[trans-4-(3,4,5-Trifluorophenyl]cyclohexyl]-2-methylspiro[3.3]heptane[sic]

6-[trans-4-(3,4,5-Trifluorophenyl]cyclohexyl]-2-ethylspiro[3.3]heptane[sic], C 62 I

6-[trans-4-(3,4,5-Trifluorophenyl]cyclohexyl]-2-propylspiro[3.3]heptane[sic], C 47 N (44.7) I

6-[trans-4-(3,4,5-Trifluorophenyl]cyclohexyl]-2-butylspiro[3.3]heptane[sic], C 56 I

6-[trans-4-(3,4,5-Trifluorophenyl]cyclohexyl]-2-pentylspiro[3.3]heptane[sic], C 55 N (41.5) I

6-[trans-4-(3,4,5-Trifluorophenyl]cyclohexyl]-2-hexylspiro[3.3]heptane[sic]

6-[trans-4-(3,4,5-Trifluorophenyl]cyclohexyl]-2-heptylspiro[3.3]heptane[sic]

6-(3,4,5-Trifluorobiphenyl-4'-yl)-2-methylspiro[3.3]-heptane

6-(3,4,5-Trifluorobiphenyl-4'-yl)-2-ethylspiro[3.3]-heptane

6-(3,4,5-Trifluorobiphenyl-4'-yl)-2-propylspiro[3.3]-heptane, C 27 N(12.1) I

8-[(3,4,5-Trifluorophenyl)cyclohexyl)]-2-propyldispiro-[3.1.1.3]decane,C 41 N (43.5) I

6-(4-Ethoxyphenyl)-2-propylspiro[3.3]heptane, C 6 N (4.9) I

6-(4-Ethoxyphenyl)-2-butylspiro[3.3]heptane

6-(4-Ethoxyphenyl)-2-ethylspiro[3.3]heptane

6-(4-Ethoxyphenyl)-2-methylspiro[3.3]heptane

6-(4-Methoxyphenyl)-2-propylspiro[3.3]heptane

6-(4-Methoxyphenyl)-2-butylspiro[3.3]heptane

6-(4-Methoxyphenyl)-2-ethylspiro[3.3]heptane

6-(4-Methoxyphenyl)-2-methylspiro[3.3]heptane

6-(4-Propoxyphenyl)-2-propylspiro[3.3]heptane

6-(4-Pentylphenyl)-2-propylspiro[3.3]heptane

Example 3 7-(3,4,5-Trifluorophenyl)-2-methylspiro[3.5]nonane

3A) 7-(3,4,5-Trifluorophenyl)-1,1-dichlorospiro[3.5]-nonane

0.1 mol of 4-methylene-1-(3,4,5-trifluorophenyl)-cyclohexane (obtainableby reacting 3,4,5-trifluorophenylmagnesium bromide with the monoethyleneketal of cyclohexane-1,4-dione followed by elimination of water,hydrogenation and ketal cleavage) and 0.1 mol of trichloroacetylchloride are reacted in accordance with Example 1B.

After reaction with zinc in accordance with Example 1C and withtriphenylmethylene phosphine in accordance with Example 1D andhydrogenation in accordance with Example 1E the product is obtained.

The following are prepared analogously:

7-(3,4-Difluorophenyl)-2-methylspiro[3.5]nonane

7-(3,4-Difluorophenyl)-2-propylspiro[3.5]nonane

7-(3,4-Difluorophenyl)-2-pentylspiro[3.5]nonane

7-(3,4,5-Trifluorophenyl)-2-pentylspiro[3.5]nonane, C 3 I

7-[trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-2-methylspiro[3.5]nonane

7-[trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-2-propylspiro[3.5]nonane

7-[trans-4-(3,4,5-Trifluorophenyl)cyclohexyl]-2-pentylspiro[3.5]nonane

Example 4 6-(3,4,5-Trifluorophenyl)-2-(trans-4-propylcyclohexyl)-spiro[3.3]heptane

4A) 3-(trans-4-Propylcyclohexyl)-2,2-dichlorocyclobutanone

A mixture of 0.25 mol of trans-4-propyl-1-vinylcyclohexane (preparedaccording to WO 88/02357) and 800 ml of diethyl ether is reacted withtrichloroacetyl chloride in accordance with Example 1B.

4B ) 3-(trans-4-Propylcyclohexyl)cyclobutanone

0.1 mol of 4A is treated with 0.4 mol of zinc powder in analogy toExample 1C.

4C ) 3-(trans-4-Propylcyclohexyl)-1-methylenecyclobutane

0.05 mol of 4B is reacted with 0.07 mol of triphenylmethylenephospine inanalogy to Example 1D.

4D ) 2-(trans-4-Propylcyclohexyl]-5,5-dichlorospiro[3.3]-heptan-6-one[sic]

35 mmol of 4C are reacted with trichloroacetyl chloride in analogy toExample 1B.

4E) 2-(trans-4-Propylcyclohexyl)spiro[3.3]heptan-6one

25 mmol of 4D are treated with zinc in analogy to Example 1C.

4F)2-(trans-4-Propylcyclohexyl)-6-hydroxy-6-(3,4,5-trifluorophenyl)spiro[3.3]heptane

A mixture of 15 mmol of 3,4,5-trifluorophenylmagnesium bromide (preparedfrom 3,4,5-trifluorobromobenzene and magnesium turnings), 15 mmol of 4Eand 50 ml of diethyl ether is stirred for 15 hours. After conventionalwork-up the product is obtained, which is processed further withoutpurification.

4G)2-(trans-4-Propylcyclohexyl)-6-(3,4,5-trifluorophenyl)spiro[3.3]hept-5-ene

A mixture of 12 mmol of 4F, 100 ml of toluene and 0.5 g ofp-toluenesulfonic acid is heated on a water separator for 10 hours.After conventional work-up the product is obtained, which is processedfurther without purification.

4H) 10 mmol of 4G are hydrogenated in accordance with Example 1E. Afterconventional work-up the product is obtained, C 46 N (61.4) I.

The following are prepared analogously:

6-(3,4-Difluorophenyl)-2-(trans-4-propylcyclohexyl)spiro-[3.3]heptane

6-(3,4-Difluorophenyl)-2-(trans-4-ethylcyclohexyl)spiro-[3.3]heptane

6-(3,4,5-Trifluorophenyl)-2-(trans-4-ethylcyclohexyl)spiro[3.3]heptane

6-(4-Trifluoromethoxyphenyl)-2-(trans-4-propylcyclohexyl)spiro[3.3]heptane,C 67 N (95.2) I

(6-(4-Difluoromethoxy-3,5-difluorophenyl)-2-(trans-4-propylcyclohexyl)spiro[3.3]heptane[sic], C 43 N (77.5) I

6-(4-Cyanophenyl)-2-(trans-4-propylcyclohexyl)spiro[3.3]-heptane, C 113N (162) I

6-(4-Ethoxyphenyl)-2-(trans-4-propylcyclohexyl)spiro[3.3]heptane

Example 5 ##STR22## are added in each case one of the followingcompounds: ##STR23##

The physical data of the resulting mixtures can be taken from Table I:

                  TABLE I                                                         ______________________________________                                                Clear Point              Viscosity                                            (°C.)                                                                          Δε                                                                       Δn                                                                              (mm.sup.2 · s.sup.-1)               ______________________________________                                        B         91        +5.2     0.094 15.0                                       B + (a)   71        n.m.     0.085 15.8                                       B + (b)   86        5.5      0.092 14.8                                       B + (c)   69        5.0      0.084 14.2                                       B + (d)   68        5.2      0.084 13.9                                       B + (e)   87        5.4      0.092 15.6                                       B + (f)   83        5.8      0.097 14.9                                       B + (g)   83        5.5      0.091 15.0                                       B + (h)   90        5.2      0.094 14.4                                       B + (i)   98        6.2      0.102 17.7                                       B + (j)   80        4.5      0.092 14.2                                       B + (k)   84        5.4      0.091 15.4                                       ______________________________________                                    

The compounds according to the invention generally achieve a loweroptical anisotropy, a lower clear point and a lower viscosity.

We claim:
 1. A cyclobutane benzene compound of formula I ##STR24## inwhich R¹ is alkyl or alkenyl having 1 to 16 carbon atoms, in whichadditionally one or more CH₂ groups may be replaced by --O--, or is agroup of the formula ##STR25## in which R² is alkyl or alkenyl having 1to 16 carbon atoms, ##STR26## o is 0 or 1, V and W are each CH₂ or CH₂CH₂, and when V is CH₂ CH₂ m is 1, 2 or 3 and W is CH₂,A¹ is eachindependently 1,4-phenylene which is unsubstituted or substituted by 1to 2 fluorine atoms, in which, in addition, one or two CH groups may bereplaced by N, or is 1,4-cyclohexylene which is unsubstituted orsubstituted by a cyano group, and in which, in addition, one or two CH₂groups may be replaced by O or S, or is thiadiazole-2,5-diyl,1,4-bicyclo[2.2.2]octylene, or a radical of the formula ##STR27## inwhich r and s are each 0, 1, 2 or 3, L¹ and L² are each F, Z¹ is--CO--O, --O--CO--, --CH₂ O--, --OCH₂ --, --CH₂ CH₂ --, --C≡C-- or asingle bond, Y is NCS, halogen or an alkyl, alkoxy, alkenyl oralkenyloxy group having 1 to 8 carbon atoms which is substituted by atleast one fluorine and/or chlorine atom, and, if m=1, 2 or 3, is CN, oralkyl or alkenyl having up to 16 carbon atoms, in which, in addition, 1or more CH₂ groups may be replaced by --O--, m is 0, 1, 2 or 3, and n is0, 1 or
 2. 2. A compound according to claim 1, in which m is
 0. 3. Acompound according to claim 1, in which V is CH₂.
 4. A compoundaccording to claim 3, of the formula I1 ##STR28##
 5. A compoundaccording to claim 4, of the formula I2 ##STR29##
 6. A compoundaccording to claim 1, of the formula I3 ##STR30##
 7. A compoundaccording to claim 6, of the formula I3a ##STR31##
 8. Aliquid-crystalline medium containing at least two liquid-crystallinecomponents, wherein at least one component is at least one compound offormula I according to claim
 1. 9. An electrooptical display containinga liquid-crystalline medium according to claim
 8. 10. A spiro heptanebenzene compound of formula I' ##STR32## wherein R¹ is alkyl or alkenylhaving 1 to 16 carbon atoms, in which additionally one or more CH₂groups may be replaced by --O--, or is a group of the formula ##STR33##in which R² is alkyl or alkenyl having 1 to 16 carbon atoms, ##STR34## ois 0 or 1; Y is NCS, halogen or an alkyl, alkoxy, alkenyl or alkenyloxygroup having 1 to 8 carbon atoms which is substituted by at least onefluorine and/or chlorine atom, CN, or alkyl or alkenyl having up to 16carbon atoms, in which one or more CH₂ groups are optionally replaced byO; andL¹ is H or F.
 11. A liquid-crystalline medium containing at leasttwo liquid-crystalline components, wherein at least one component is atleast one compound of formula I' according to claim
 10. 12. Anelectrooptical display containing a liquid-crystalline medium accordingto claim 11.